title: MiR-34a is up-regulated in response to low dose, low energy X-ray induced DNA damage in breast cells.
abstract: BACKGROUND
  MicroRNAs are non-coding RNAs involved in the regulation of gene expression including DNA damage responses. Low doses of low energy X-ray radiation, similar to those used in mammographic exams, has been described to be genotoxic. In the present work we investigated the expression of miR-34a; a well described p53-regulated miRNA implicated in cell responses to X-ray irradiation at low doses.
  
  
  METHODS
  Non-cancerous breast cell line MCF-10A and cancerous T-47D and MCF-7 cell lines were submitted to a low-energy X-ray irradiation (ranging from 28-30 Kv) using a dose of 5 Gy. The expression level of miR-34a, let-7a and miR-21 was assessed by qRT-PCR at 4 and 24 hours post-irradiation. DNA damage was then measured by comet assay and micronuclei estimation in MCF-10A and MCF-7 cell lines, where an increase of miR-34a levels could be observed after irradiation. The rate of apoptotic cells was estimated by nuclear staining and fluorescence microscopy. These experiments were also performed at low doses (3; 12 and 48 mGy) in MCF-10A and MCF-7 cell lines.
  
  
  RESULTS
  We have observed an increase in miR-34a expression 4 hours post-irradiation at 5 Gy in MCF-10A and MCF-7 cell lines while its level did not change in T-47D, a breast cancer cell line bearing non-functional p53. At low doses, miR-34a was up-regulated in non-tumoral MCF-10A to a higher extent as compared to MCF-7. MiR-34a levels decreased 24 hours post-irradiation. We have also observed DNA damage and apoptosis at low-energy X-ray irradiation at low doses and the high dose in MCF-10A and MCF-7 4 and 24 hours post-irradiation relative to the mock control.
  
  
  CONCLUSIONS
  Low energy X-ray is able to promote DNA strand breaks and miR-34a might be involved in cell responses to low energy X-ray DNA damage. MiR-34a expression correlates with X-ray dose, time after irradiation and cell type. The present study reinforces the need of investigating consequences of low dose X-ray irradiation of breast cells.
authors.affiliation: Departamento de Genética, Universidade do Estado do Rio de Janeiro, Instituto de Biologia Roberto Alcantara Gomes, 20550-013 Rio de Janeiro, Brazil. claudia.gallo@pq.cnpq.br.
authors.forename: Luiza
authors.initials: L
authors.lastname: Stankevicins
authors.forename: Ana Paula
authors.initials: AP
authors.lastname: Almeida da Silva
authors.forename: Flavia
authors.initials: F
authors.lastname: Ventura Dos Passos
authors.forename: Evelin
authors.initials: E
authors.lastname: Dos Santos Ferreira
authors.forename: Maria Cecilia
authors.initials: MC
authors.lastname: Menks Ribeiro
authors.forename: Mariano
authors.initials: M
authors.lastname: G David
authors.forename: Evandro
authors.initials: E
authors.lastname: J Pires
authors.forename: Samara Cristina
authors.initials: SC
authors.lastname: Ferreira-Machado
authors.forename: Yegor
authors.initials: Y
authors.lastname: Vassetzky
authors.forename: Carlos Eduardo
authors.initials: CE
authors.lastname: de Almeida
authors.forename: Claudia Vitoria
authors.initials: CV
authors.lastname: de Moura Gallo
mesh_terms: D017209:Apoptosis / Q000528:radiation effects; D001940:Breast / Q000528:radiation effects*; D001943:Breast Neoplasms / Q000235:genetics*; D045744:Cell Line, Tumor; D002478:Cells, Cultured; D020552:Comet Assay; D004249:DNA Damage / Q000528:radiation effects*; D005260:Female; D006801:Humans; D035683:MicroRNAs / Q000096:biosynthesis*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015854:Up-Regulation; D014965:X-Rays / Q000009:adverse effects*
chemical_list: C522425:MIRN34 microRNA, human; D035683:MicroRNAs